Contact structure for high-voltage circuit interrupter with liner components

ABSTRACT

A separable contact structure is provided for a high-voltage compressed-gas circuit interrupter involving at least one of the contacts being tubular to provide a gas flow therethrough, and having a liner component therein. To facilitate movement of the terminal end of the arc, a relatively thin tubular member is inserted interiorly of the hollow contact, and, by electrically connecting the same to the inner anterior end of the hollow contact, the magnetic field situation is such that the terminal end of the arc is encouraged to move axially along the relatively thin tubular liner member to thereby effect considerable elongation of the established arc, and thereby to effect the extinction of the same by a more effective gas flow condition. As a further extension of this same concept, a cooperable tubular contact structure may be provided, through which gas also exhausts, and a similar relatively thin tubular liner member may also be associated therewith to act in a similar manner.

United States Patent [72] Inventors Frank L. Reese Monroeville; Hayes 0.Dakin, J r., Irwin, both of, Pa. [Zl] Appl. No. 9,373 [22] Filed Feb. 6,1970 [45] Patented Sept. 7, I971 [73] Assignee Westinghouse ElectricCorporation Pittsburgh, Pa.

[54] CONTACT STRUCTURE FOR HIGH-VOLTAGE CIRCUIT INTERRUPTER WITH LINERPaterson et al. 200/148 ABSTRACT: A separable contact structure isprovided for a high-voltage compressed-gas circuit interrupter involvingat least one of the contacts being tubular to provide a gas flowtherethrough, and having a liner component therein. To facilitatemovement of the terminal end of the are, a relatively thin tubularmember is inserted interiorly of the hollow contact, and, byelectrically connecting the same to the inner anterior end of the hollowcontact, the magnetic field situation is such that the terminal end ofthe arc is encouraged to move axially along the relatively thin tubularliner member to thereby effect considerable elongation of theestablished arc, and thereby to effect the extinction of the same by amore effective gas flow condition.

As a further extension of this same concept, a cooperable tubularcontact structure may be provided, through which gas also exhausts, anda similar relatively thin tubular liner member may also be associatedtherewith to act in a similar manner.

FULLY OPEN POSITION PATENTEU SEP 71971 SHEET 1 [IF 4 SP GAS HIGHPRESSURE SF GAS LOW PRESSURE SP6 GAS.

INVENTORS Frank L. Reese a Hayes Q Dokin, Jr. BY

1e ATTORNEY PATEHTED SEP 7197i SHEET 2 [IF 4 FIG.4

CLOSED POSITION 8 PATENTEDSEP mm 3.603754 SHEET u 0F 4 Fig. 5

FULLY OPEN POSITION CONTACT STRUCTURE FOR HIGH-VOLTAGE CIRCUITINTERRUPTER WITH LINER COMPONENTS CROSS-REFERENCES TO RELATEDAPPLICATIONS Reference may be made to U.S. Pat. application filed Dec.30,.1968, by Frank L. Reese and Hayes 0. Dakin, Jr., entitledDELAYED-ACTING BLAST-VALVE OPERATOR CON- STRUCTION, Ser. No. 787,658,and assigned to the assignee of the instant application.

BACKGROUND OF THE INVENTION The present invention is particularlyconcerned with the separable contact structure applicable to ahigh-voltage compressed-gas circuit interrupter. As set forth in theaforementioned U.S. Pat. application, Ser. No. 787,658, for a particulartype of compressed-gas circuit interrupter, there is involved a pair ofseparable contacts, each of which is tubular and permits the exhaustingof gas flow therethrough to effect arc interruption therein. Actually,in the aforesaid construction, the movable contact, in effect,constitutes a primary blast-valve separating a high-pressure gaseousregion, located externally of the contact structure, from the relativelylow-pressure region provided interiorly of the separable contactstructure. When it is desired to open the circuit interrupter, themovable contact structure is withdrawn from the stationary contact,thereby performing two functions. The first function is the opening of aso-called primary blast valve at the contacts, and the second functionis the establishment of an are between the movable and the separablestationary contact structures. The radially inwardly directed gas flowrapidly carries the terminal ends of the are within the separatedtubular contact structures, and effects a lengthening of the terminalends of the are within the separable tubular contact structures untilinterruption is achieved. Reference may be had to the aforesaid U.S.Pat. application Ser. No. 787,658 for a general description of such atype of separable contact structure and its operation, the aforesaidapplication relating its use to a new line of highvoltage circuitinterrupters, accommodating a wide variety of current and voltageratings.

In the fabrication of relatively heavy castings for the contactstructures, heretofore use has been made of Cupaloy" which is aregistered trademark of the Westinghouse Electric Corporation, andrefers to an alloy of copper. Difficulty has, however, been encounteredwith porosity of the castings which permitted leakage of high-pressuregas exteriorly of the separable contact structure interiorly into theregion disposed within the separable contact structure, in addition, theuse of this alloy Cupaloy was quite expensive.

In an effort to provide a substitute for the alloy Cupaloy," attempt hasbeen made to use aluminum, either using permanent mold castings, orordinary castings. However, aluminum has a relatively low meltingtemperature, as contrasted with Cupaloy, and consequently protection isneeded to prevent the pitting, erosion or other deterioration resultingfrom the movement of the terminal ends of the hot are within theseparable contact structures.

SUMMARY OF THE INVENTION According to the present invention, a moreeffective gas flow and are movement is provided by the insertion withinat least one of the separable tubular contacts of a relatively thintubular member, preferably being made of a magnetic material, such asstainless steel, or steel. Preferably, the construction is such that theinner end of the relatively thin tubular member is electrically attachedto the inner anterior extremity of the movable tubular contact, so thata magnetic field is set up, which is favorable to are elongation withinthe separable tubular contact structure. In addition, the structure hasthe advantage that a relatively cheap material, such as aluminumcastings, may be employed in the fabrication of the maincontact-supporting structure. Due to the relatively high meltingtemperature of the relatively thin tubular member of stainless steel, orsteel, there arises the advantage of a resistance to are erosion of therelatively thin tubular member.

Accordingly, a general object of the present invention is the provisionof an improved separable contact structure for a compressed-gas circuitinterrupter, which is of a relatively inexpensive construction by usinga relatively cheap material, such as aluminum, of lightweight, and alsofavorable to the considerable elongation of the arc terminals within theseparable tubular contact structure, while being subjected to effectivegas flow conditions.

Another object of the present invention is the provision of an improvedseparable contact for a high-voltage compressed gas circuit interrupterin which are elongation is magnetically encouraged by a linerconstruction where magnetic looping of the arc is encouraged.

A further object of the present invention is the provision of animproved, relatively cheap, and lightweight contact structure for ahigh-voltage circuit interrupter, in which arc elongation is encouraged,and are extinction is thereby facilitated.

An auxiliary object of the present invention is the provision of arelatively cheap separable tubular contact construction for acompressed-gas circuit interrupter, in which the magnetic fields arecontrolled in an advantageous manner to encourage axial elongatingmovement of the arc terminals within the separable tubular contactstructure. Obviously, this facilitates arc extinction in a much shortertime than would parent upon reading the following specification, takenconjunction with the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is an end elevational view of athree-phase compressed-gas circuit interrupter embodying the principlespf the present invention;

FIG. 2 is a vertical sectional view, partially in side elevation, of theinterrupter assemblage associated with the circuit interrupter of FIG.1, and extending upwardly from the left-hand side thereof;

FIG. 3 is a side elevational view of the three-phase circuit interrupterof FIG. I, as viewed from the side indicated by the arrows A-A of FIG.1;

FIG. 4 is a considerably enlarged sectional fragmentary view of theseparable contact structure, the contact structure being illustrated inthe closed-circuit position;

FIG. 5 is a view somewhat similar to that of FIG. 4, but illustrating,in full lines, the separable contact structure in its fully open-circuitposition, with the dotted lines illustrating the intervening contactpositions, in which are establishment is initiated and elongated;

FIG. 6 illustrates, in an enlarged manner, a side elevational view ofthe relatively thin liner-tube structure, which is utilized in thepresent invention, and inserted within the cpntact structure; I

FIG. 7 is a sectional view taken along the line VII-VII of FIG. 4; and,

FIG. 8 is a diagrammatic view illustrating the principles of the presentinvention.

A l DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to the drawings,and more particularly to FIGS. l-3 thereof, the reference numeral 1generally designates a three-phase circuit breaker. As shown in FIGS.1-3, it will be apparent that the circuit breaker structure 1 issupported by a metallic framework 2, which may be composed of heavyangle-iron braces 3 and beams 4. The circuit breaker structure I. is,generally, of the dual-pressure type involving the use of a suitablearc-extinguishing gas 5 at two different pressure levels, namely a highpressure, say 230 p.s.i., suitable for use for injecting into the are 6(FIG. 5) to effect the extinction thereof, and, additionally, being usedin the operating mechanism 7 (FIG. 3), to effect actuation of a pistonstructure (not shown) associated with the arc-extinguishing unit 9 (FIG.2). The reference numeral 10 designates the piston rod in FIG. of thedrawings, which actuates the movable contact assemblage l 1 in theopening and closing movements.

The second pressure level, associated with the arc-extinguishing unit 9,is of a relatively low pressure, say 5 p.s.i., for example, and ispresent interiorly of the contact structure 13 (FIG. 2) in theclosed-circuit position thereof within the region 15, as illustrated inFIG. 4 of the drawings.

Generally, as shown in FIG. 3, the several pole-units A, B and C arespaced laterally apart upon the grounded supporting framework 2, and aremechanically interconnected to a common mechanism 17 at groundpotential. The ground mechanism 17 is described in detail in US. Pat.application filed Nov. 18, I968, Ser. No. 776,510, by William H. Fischerand Wayne S. Aspey and assigned to the assignee of the instantapplication.

Briefly, the manner of operation of the circuit breaker structure 1 issuch as to cause the actuation of a ground potential operator 17 toeffect motion of a mechanical linkage 19, which interconnects theseveral three-way valve control rods 20, extending upwardly,individually, within the three arcextinguishing assemblages 22, moreclearly shown in FIG. 2 of the drawings. As illustrated in FIG. 2 of thedrawings, the valve control rod 20, moving only a short distance,extends upwardly within insulating supporting tubes 24, 25 disposedinteriorly of an insulating inner tension tube 27 serving to spatiallyrelate the one or more pairs of contact structures 13, which may beemployed.

As shown in FIG. 2, only a single pair of separable contact structures13 is utilized; however, for higher voltages and higher ratings, aplurality of pairs of contact structures 13 may be utilized, if desired.

Generally, the arc-extinguishing assemblage 22 comprises an outerinsulating weatherproof casing 29, which may be formed either ofporcelain, or of a suitable resinous material serving to enclose thearc-extinguishing structure 9 of the interrupter I. Thearc-extinguishing structure, or assemblage 22, is supported upon thegrounded housing 31 and is slanted, or canted away from a terminalbushing structure 33, which serves to cause the current path to beconducted in a generally U-shape, as indicated by the dotted line 34(FIG. I). The terminal bushing structure 28 (FIG. 1) generally, has aterminal rod 35 at high voltage extending therethrough, and is spacedwithin an outer weatherproof casing 36 composed of a suitable insulatingmaterial, such as porcelain. A suitable arc-extinguishing gas, which hashigh qualities, may be enclosed within the terminal bushing structure 33at a relatively low pressure, say of 25 psi. This gas may be the samegas 5 as described heretofore, such as SF but at a much lower pressure.

FIG. 2 shows a vertical cross-sectional view taken through theinterrupting structure 9 of a single pole-unit A of the three-phasecircuit interrupter I. As well known by those skilled in the art, thereare three such structures A, B, and C to control the three phases of atransmission system.

In the circuit breaker structure 1 under consideration, a suitablehighly effective arc-extinguishing gas 5, such as sulfurhexafluoride (SPgas, may be used as the arc-extinguishing gas, and also as an insulatinggas to enable a close spacing of the live parts. It is also used as theinsulating gas within the terminal bushing structure 33. US. Pat.2,757,261 describes the arc-extinguishing characteristics of thisparticular gas 5.

As mentioned hereinbefore, generally, the manner of operation of thecircuit interrupter is the simultaneous actuation of the three valvecontrol tripping rods 20, which extend upwardly into the top of thearc-extinguishing assemblages 22. As described in the aforesaid Pat.application Ser. No. 787,658, the valve control tripping rods 20 actuatethree-way control valves 37 to their operating position to admit ahighpressure gas below piston structures (not shown), which effectupward movement of the operating rods (FIG. 5), at 1 consequently upwardopening movement of the separable contact structure 13. As illustratedin F IG. 5, the piston structure, not shown, is mechanically tied, bymeans of a piston rod 10, to a generally ladder-shaped structure 39,which comprises a pair of laterally spaced insulating operating rods 41,which extend axially of the arc-extinguishing assemblage 22 through apair of hollow supporting tubes 42.

The region 44, immediately adjacent the contact structure 13, andexternally thereof in the closed-circuit position, as illustrated inFIG. 4, is at a relatively high pressure, say 230 psi, as more clearlydescribed in US. Pat. application Ser. No. 759,992, filed Sept. 16,1968, by Lee E. Berkebile, the arc-extinguishing structure, or unit 9being of the so-called downstream type, in which high-pressure gas 5moves radially into and through the separated contact structure 13during the opening operation, until the flow of gas is halted by theclosing operation of a pair of downstream, or secondary blast-valves,indicated by the reference numerals 46 and 47 in FIGS. 4 and 5 of thedrawings. 5

MOVABLE CONTACT STRUCTURE (l 1) As briefly pointed out hereinbefore, themovable contact assemblage 39 comprises a generally ladder-shapedmovable structure secured at its upper end to a yoke-shaped member, notshown, which, in turn, is mechanically adjustably secured, as at 10a, tothe movable tubular contact 49. A pair of spaced insulating sideoperating rods 41, constituting a portion of said ladder-shapedstructure 39, extend interiorly of hollow insulating supporting tubes42, serving to space the interrupting units 9 axially apart, when aplurality of such units are used.

With reference being directed particularly to FIG. 5 of the drawings, itwill be observed that the piston rod 10 is adjustably secured, as at10a, to the hollow movable contact 49. The side operating rods 41additionally are secured to a movable blast-valve activator 50 having aconfiguration more clearly shown in FIG. 5 of the drawings, and morefully described hereinafter. 1

The moving contact 49 makes separable engagementwith a movable hollowsealing structure 52 (FIG. 5), which is supported by a stationary hollowcontact structure 53, which is fixably supported upwardly from a basesupport 55. As shown in more detail in FIG. 5 of the drawings, anexhausting flow of arcextinguishing fluid 5, at high pressure, occursacross the are 6, and diametrically in opposite directions through theinterior of both the movable and stationary hollow contacts 49, 53, asindicated by the arrows 56 in FIG. 5.

Generally, there is provided a primary blast-valve 58 (FIG. 4)constituted by the lower tip portion 49a of the movable contact 49making abutting engagement with a relatively stationary primaryblast-valve seat 52a resiliently supported upon the stationary contactsupport 55, as shown in FIG. 5. A compression spring 59 provides adesired contact pressure there between, and provides for a limitedamount of overtravel of the movable contact 49. Additionally, there isprovide a plurality of circumferentially disposed stationary contactfingers 61, which make contacting engagement with the external side 49bof the movable tubular contact 49.

In addition to the primary blast-valve support, there is provided a pairof secondary downstream blast-valves 46, 47, which are closed near theend of the opening operation, as described more clearly hereinafter.

In the arrangement of FIG. 5, it will be noticed that there is provideda double-exhausting flow of gas, inasmuch as both the stationary andmovable contacts 49, 53 are hollow, and provide for exhaust outletstherethrough. However, for higher voltage ratings, where a double-breakis desired, additional arc-extinguishing units 9 may be provided asshown in US. Pat. application (W.E. 39,242).

LATCHING STRUCTURE FOR THE SECONDARY BLAST VALVES (46, 47)

The circuit interrupter l of the present invention provides a means foroperating the secondary blast-valves 46, 47. On the circuit breaker ofthe present invention, as previously pointed out, a gas-operated pistonmechanism 7 is used to open and to close the movable contacts 49 of theinterrupter 1.

The movable contact 49 of the interrupter forms a seal with a relativelystationary primary blast-valve seat 52a (FIG. 5) constituting a primaryblast-valve 58, so that when the breaker contacts 49 are closed, theseal 52a at the primary blast-valve 58 prevents the high-pressure gasfrom flowing into the center of one or both of the moving separablecontacts 49, 53. At this time, the secondary blast-valves 46, 47 areopen. When the moving contact 49 opens, during the opening operation,the secondary blast-valves 46, 47 are going closed to stop theexhausting gas flow into the low-pressure region 15.

In the circuit-interrupter construction as described, it is desirablethat when the contacts 49 of the interrupter open, they arrive in thefully open-circuit position in the shortest period of time. The openposition can be reached while there is still an are 6 between thecontacts 49, 53. It is quite necessary that the secondary blast valves46, 47 remain open at this time to allow gas flow to interrupt the are6. Hence, the secondary blast-valve closing must have a travel curve,which is delayed from that of the moving contacts 49. The followingdeals with a means of delaying the secondary blast-valve travel.

With reference to FIGS. 4 and 5, it will be observed that the tubularmoving contact 49 is directly connected to the mechanism 7, and has acertain travel characteristic. The blast-valve activator 50 is alsodirectly connected to the movable contact 49, and has hence,consequently, the same travel. As the movable contact 49 moves to theopen position, the blast-valve activator 50 starts compressing acompression spring 63. This compression spring 63 becomes loaded, sincethe opposite spring seat 64 is prevented from moving, since this springseat 64 is a part of the blast-valve device, and the blast-valve isprevented from moving by two latches 66 (FIG. 5), which are spaced 180apart. There is some free movement of the activator 50 before startingto compress the compression spring 63, since it is necessary to keep theload on the operating mechanism 7 to a minimum when starting the openingmotion. After the activator 50 has moved a specific distance, andthereby compressed the spring 63, protrusions 500 on the activator 50hit a raised surface 68 on the latches 66, thereby causing the latches66 to move back, and allow the secondary blast-valves 46, 47 to goclosed, with a travel curve, which is delayed as compared to that of themoving contact 49. When the secondary blast-valve 46, 47 is closed,there is some compression on it due to the position of the activator 50compressing the spring 63, additionally due to an inner spring 69,inside blast valve 46, and basic mounting plate number 70, plus adifferential pressure holding it closed, due to the geometry of theblast-valve face.

When the circuit breaker contacts 49 are being closed, the secondblast-valves 46 and 47 are closed. The activator 50 with its rubberbumper 71 strikes the secondary blast-valve 46, and moves it to the openposition. A small gas dashpot is also formed between the activator 50and the blast valve 46 to help reduce the shock. At this time, thelatches 66 fall under the shoulders 460 (FIG. 5) and the blast-valve 46is ready for another contact opening operation.

The pneumatic mechanism 7, disposed within the cap structure andconcerning the dual action of the piston is set forth and claimed in theUS. Pat. application filed Dec. 10, 1968, Ser. No. 782,631, by WilliamH. Fischer and Wayne S. Aspey, and assigned to the assignee of thepresent invention.

The exhausting gas flow during the opening operation is collected inlow-pressure chambers and eventually is conducted by means of the hollowoperating rod tube down to the lowpressure tank 72 (FIG. 3) at the baseof the supporting framework 2. A suitable compressor, not shown, is usedto recompress the gas to the high-pressure level of 220 p.s.i., forexample.

As mentioned hereinbefore, in the aforesaid construction of the gascircuit breaker, a general method of interrupting the are is todischarge gas 5 through moving or stationary cylindrical contactstructures 49, 53, which form the contacts of the interrupter 9. Thematerials used for the cylindrical contact structures are usuallycopper, or a copper alloy, such as "Cupaloy," due to the requirements ofgood electrical conductivity plus having a high melting temperature,since the are 6 can impinge on the interval walls of the tubular contactstructure 49 or 53.

The copper alloy Cupaloy is an alloy of copper, the trademark beingowned by the Westinghouse Electric Corporation, and containing as alloycomponents 0.01 percent5 percent silver (Ag), 0.05 percent-5 percentchromium (Cr), and the balance being copper (Cu).

The present invention is particularly concerned with the use ofthin-walled cylinders of stainless steel, or steel, or other conductingmagnetic material, which can be inserted within the main contactstructural members These thin-walled cylinders can be made of a highmelting material, such as stainless steel, other than copper, which canbe easily fabricated.

The relatively thin metallic liners of the present invention may beformed of an easily fabricated material, such as stainless steel; or theliners may be made of steel with a coating of nickel. It has been foundthat previously, the heavy castings of Cupaloy" had a high porosity, incertain instances, which lead to a leakage of gas flow from the highpressure region 44 through the castings and into the relativelylow-pressure re gion l5 interiorly of the separable tubular contacts4953. To avoid the problem of porosity, when using Cupaloy, and toprovide a relatively inexpensive substitution therefor, such as thematerial aluminum, we have found it desirable to utilize a protectiveliner, such as the slotted tubular liner 80, or the two liners and81-82, such as set forth in FIG. 5 of the drawings. The structuralsupport casting 73-75 are preferably made out of aluminum to providegood conductivity, lightweight, and the possibility of using permanentmold castings for an inexpensive construction, avoiding the problem ofporosity. These contact liners 80, 81, 82 are shown in more detail inFIGS. 4 and 5 of the drawings.

COMPARISON OF MELTING TEMPERATURE less Desirable ls Less DesirableBecause of Probable Nickel Coating needed counteracting Heat andCorrosion Pure Copper 1,083 "C Another use can be made of theserelatively thin metallic arc chamber liners 80, 81, 82. If one end ofthese liners is electrically insulated from the supporting structuralcasting, the flow of current from the arc terminals can be directed,such that the arc length can be increased by using the magnetic loopformed by this current flow. FIG. 8 of the drawings more clearlyillustrates this principle, which, to a certain extent, is somewhatsimilar to the use of arcing horns in airbreak circuit interrupters. Aswell known by those skilled in the art, a magnetic loop circuit isdeveloped, and the magnetic interaction caused by the are 6 and currentflow through the conducting members 80, 81, 82 is such as to loop theare into an ever-expanding length. This same phenomena can be utilizedin the contact structure of the present invention by connecting therelatively thin-walled tubes 80, 81, 82 in good conductive manner to theinner anterior ends of the relatively stationary and movable tubularcontacts 49, 53.

FIG. 8 shows a modified contact structure using the aforesaid principle.With metallic cylinder 90 connected to the movable contact at point B,"the current must flow through this point B regardless of where the arc 6impinges upon the metallic cylinder 90. The magnetic forces, caused bythis loop of current, forces the are 6 to lengthen thereby increasingthe efficiency of arc interruption. Members 90 and 91 of FIG. 8 can beslotted to provide additional control of the current flow, if desired.

From the foregoing description it will be apparent that there has beenprovided an improved separable contact structure for a high-voltagecompressed-gas circuit interrupter, in which the moving contact partscan be made of lightweight material, for example aluminum casting, andthe liners 80, 81, 82 utilized of a high melting point material, such ascoated steel or stainless steel, and the arc lengthening 6 can bethereby encouraged magnetically by the magnetic loop effect encountered.

Although there has been illustrated and described specific structures,it is to be clearly understood that the same was merely for the purposeof illustration, and that changes and modifications may readily be madetherein by those skilled in the art, without departing from the spiritand scope of the invention.

We claim:

1. A gas-blast circuit interrupter including a pair of separable arcingcontacts at least one of which is hollow, means for seperating saidseparable contacts to establish arcing, means for forcing a radiallyinwardly flow of gas between the contacts to exhaust through said onehollow arcing contact, and a relatively thin metallic tubular linermember disposed interiorly of said one hollow arcing contact to protectthe inner surfaces thereof from the effects of arcing whereby arelatively cheap, low melting temperature material may be used forfabrication of said one hollow arcing contact.

2. The combination of claim 1, wherein the relatively low meltingtemperature material is aluminum or an alloy thereof.

3. The combination of claim 1, wherein the relatively thin metallictubular liner member is essentially steel.

4. The combination of claim 1, wherein both arcing contacts are hollow,and both have relatively thin tubular metallic liner members therein toprotect the inner surfaces of the arcmg contacts.

5. The combination of claim 1, wherein the liner member is electricallyconnected to the anterior end of the hollow arcing contact and insulatedfrom the posterior end thereof, so that a magnetic loop effect isachieved to magnetically promote arc elongation.

6. The combination of claim 4, wherein both liner members areelectrically connected to the anterior ends of the respective hollowarcing contacts to achieve a magnetic arc-looping effect.

7. A gas-blast circuit interrupter including a relatively tubularmovable sleevelike contact cooperable with a stationary contact toestablish an arc, a primary blast-valve effect being achieved by theclosure of the movable tubular contact, means generating a high-pressuregaseous region exteriorly of the contacts in the closed position and arelatively low-pressure gaseous region interiorly of the contacts atthis time, and a relatively thin metallic tubular liner member disposedinteriorly of said one hollow arcing contact to protect the innersurfaces thereof from the effects of arcing, whereby a relatively cheaplow melting temperature material may be used for fabrication of said onehollow arcing contact.

8. The combination of claim 7, wherein both contacts are hollow and bothare protected by individual relatively thin metallic liner members.

9. The combination of claim 7, wherein means provide a secondaryblast-valve for the exhausting of gas through the movable tubularcontact, and said means closes the secondary blast-valve at the end ofthe opening 0 era tion.

10. The combination of claim 9, w erein said means opens the secondaryblast-valve in the closed contact position.

1. A gas-blast circuit interrupter including a pair of separable arcingcontacts at least one of which is hollow, means for seperating saidseparable contacts to establish arcing, means for forcing a radiallyinwardly flow of gas between the contacts to exhaust tHrough said onehollow arcing contact, and a relatively thin metallic tubular linermember disposed interiorly of said one hollow arcing contact to protectthe inner surfaces thereof from the effects of arcing whereby arelatively cheap, low melting temperature material may be used forfabrication of said one hollow arcing contact.
 2. The combination ofclaim 1, wherein the relatively low melting temperature material isaluminum or an alloy thereof.
 3. The combination of claim 1, wherein therelatively thin metallic tubular liner member is essentially steel. 4.The combination of claim 1, wherein both arcing contacts are hollow, andboth have relatively thin tubular metallic liner members therein toprotect the inner surfaces of the arcing contacts.
 5. The combination ofclaim 1, wherein the liner member is electrically connected to theanterior end of the hollow arcing contact and insulated from theposterior end thereof, so that a magnetic loop effect is achieved tomagnetically promote arc elongation.
 6. The combination of claim 4,wherein both liner members are electrically connected to the anteriorends of the respective hollow arcing contacts to achieve a magneticarc-looping effect.
 7. A gas-blast circuit interrupter including arelatively tubular movable sleevelike contact cooperable with astationary contact to establish an arc, a primary blast-valve effectbeing achieved by the closure of the movable tubular contact, meansgenerating a high-pressure gaseous region exteriorly of the contacts inthe closed position and a relatively low-pressure gaseous regioninteriorly of the contacts at this time, and a relatively thin metallictubular liner member disposed interiorly of said one hollow arcingcontact to protect the inner surfaces thereof from the effects ofarcing, whereby a relatively cheap low melting temperature material maybe used for fabrication of said one hollow arcing contact.
 8. Thecombination of claim 7, wherein both contacts are hollow and both areprotected by individual relatively thin metallic liner members.
 9. Thecombination of claim 7, wherein means provide a secondary blast-valvefor the exhausting of gas through the movable tubular contact, and saidmeans closes the secondary blast-valve at the end of the openingoperation.
 10. The combination of claim 9, wherein said means opens thesecondary blast-valve in the closed contact position.